The present invention relates generally to disposable food service articles such as plates, trays and the like and in preferred embodiments to food serving plates and plates formed from high modulus, mineral-filled polyolefin sheet and most preferably mineral-filled polypropylene.
Disposable articles are commonly formed with a curled lip to impart strength to a cup, canister, or carton for example, as is seen in U.S. Pat. No. 5,184,995 to Kuchenbecker. The curl tends to give the article a utilitarian look and feel, not necessarily optimally aesthetically pleasing; especially for disposable articles which can be re-used on multiple occasions such as plastic articles.
There is shown in the U.S. Pat. No. 4,578,296 of Miyazaki et al. a thermoformed article manufactured from filled polyolefin sheet. The polyolefin resin composition includes from 30 to 80 percent of resin, from 19 to 69 percent by weight talc and from 1 to 10 percent by weight titanium dioxide. An article formed from the sheet typically includes a curled lip or a severely downwardly projecting outer lip. Note column 9, line 49 through column 10, line 38.
In accordance with the present invention, there are provided disposable service articles without a curled or severely downturned flange, which features are undesirable in terms of aesthetic qualities and brittleness.
The invention is described below with reference to the attached figures which show preferred shapes and dimensions.
The plates of the present invention include in a preferred embodiment a plastic plate with a four-radius profile which balances the need for increased rigidity (strength) and rim stiffness (sturdiness) per given material weight/cost. The ergonomic rim profile provides for ease of holding and carrying, consumer friendly shape denoting Permanentware qualities, without the negative side effect of brittleness encountered when using high modulus/stiffness construction materials. The four-radius disposable plastic plate design has a curvilinear rim surface onto which patterning can be applied for visual, tactile and strength purposes. The plate design is strong but not brittle during use even with the high modulus/stiffness mica filled polypropylene (PP) plastic material.
Plates produced with other shapes were rigid but often failed by brittle cracking in the flange and downturn areas. The stresses generated in the flange and downturn areas by deflection of the product during use apparently exceeded the highly filled material strength resulting in failure. It is possible that imperfections on the product""s trimmed edge may contribute to brittle cracking by providing failure initiation points for the notch sensitive, highly filled materials preferably used in accordance with the invention and set forth in the attached Appendix.
It was discovered that plastic plates described in this invention disclosure still had exceptional strength per material weight, but also significantly reduced brittle cracking with the highly filled nonhomogeneous materials. The four-radius design, for example, would not build up the high stress levels during deflection even with trimmed edge may imperfections and was less prone to brittle cracking.
Plates having a circular configuration as illustrated employ the four-radius plastic plate design. The plastic articles of manufacture may also be square or rectangular in shape having angular comers, such as found in a tray. Further, additional plastic shapes such as triangular, multi-sided, polyhexal, etc. are contemplated including compartmented trays and oval platters.
It will be appreciated that a salient feature of the inventive articles is the smooth profile as described herein. In general, the transitions between the center, sidewall and flange of the plate are kept free of sharp bends or curves so that mechanical stresses are not concentrated beyond the ability of the material to withstand them. In addition to being operative to avoid undesirable stress regions, the profile is flowing in appearance and provides a pleasing, ergonomic hand feel.
In general, the invention is directed to disposable food contact articles formed of a polyolefin, mineral-filled sheet and have a characteristic diameter as well as a substantially planar central portion, a sidewall portion and a flange portion. For a circular article such as a plate, the characteristic diameter is simply the diameter of the plate as the term is ordinarily employed, i.e., the distance through the center between opposing outer edges of the flange. For non-circular articles, the characteristic diameter is the average distance through the center between opposing outer edges of the flange of the article. Thus, for a rectangular article the characteristic diameter is the average of the shorter side and the longer side, for an oval article the characteristic diameter is the average of the minor axis length and major axis length of the oval and so forth.
The inventive articles are characterized by a smooth profile wherein direction changes are accomplished by way of a plurality of arcuate portions, each of which has a radius of curvature. A particularly preferred embodiment is a four radius plate as described herein, characterized in that the ratio of the length of each radius of curvature to the diameter is at least about 0.02. A ratio of at least about 0.03 is preferred with a ratio of at least about 0.035 being still more preferred. Various details will become more understood by reference to the drawings and detailed description which follows.